1. Field of the Invention
The present invention relates to a method for spread spectrum communications and to a transmitter and receiver thereof, and more particularly to a method for spread spectrum communications between a base station and a mobile station and to a transmitter of the base station and a receiver of the mobile station.
2. Description of the Related Art
FIG. 1 is a block diagram of a conventional transmitter used for spread spectrum communications. In this diagram, reference numeral 8-1 denotes a transmitting baseband processing part, 8-2 a baseband modulating part, 8-3 a spread modulating part, 8-4 a power amplifying part, 8-5 a local-transmitting-frequency generating part and 8-6 a spread-code generating part. FIG. 2 illustrates respective circuits of these functional parts of FIG. 1.
The transmitting baseband processing part 8-1 functions to adapt an analog voice signal to a modulation method of the baseband modulating part 8-2. In a case of performing a narrowband frequency modulation, as shown by (a) of FIG. 2, the transmitting baseband processing part 8-1 outputs a voice input signal by passing the voice input signal through a differential circuit 9a-1, an amplitude limiter 9a-2 and a low-pass filter 9a-3. In the frequency modulation, the differential circuit 9a-1 functions to improve talk articulation and the amplitude limiter 9a-2 functions to limit frequency shifts.
In a case in which the baseband modulating part 8-2 performs a digital modulation, the transmitting baseband processing part 8-1 converts an analog input signal of, for example, voice or the like, into a digital signal, and then outputs the digital signal to the baseband modulating part 8-2.
The baseband modulating part 8-2 performs a carrier modulation according to a communication information signal of the voice, low-spead data or the like which is outputted from the transmitting baseband processing part 8-1. In a case in which the signal to be transmitted is a digital signal from the beginning like an individual connection control signal of each mobile station, the digital signal is directly inputted from a logic circuit portion (not shown) into the baseband modulating part 8-2. The baseband modulating part 8-2 modulates the inputted signal and then outputs the modulated signal to the spread modulating part 8-3.
Additionally, in a case of outputting, for example, an FM (i.e., frequency modulation) signal of 150 MHz, in the baseband modulating part 8-2, as shown by (b) of FIG. 2, a frequency modulator 9b-1 generates an FM wave of several MHz to several tens of MHz by the input information signal of the voice, data or the like. Then a frequency converter 9b-2 uses the FM wave of several MHz to several tens of MHz and a signal of a local transmitting frequency of 140 MHz to output a narrowband FM signal of 150 MHz.
In a case of performing a digital modulation such as FSK or the like, the baseband modulating part 8-2 shifts a transmitting frequency to a plus direction or a minus direction according to the digital input signal of the voice, data, or the like.
The spread modulating part 8-3 spreads the signal (for example, the FM wave of 150 MHz, or the like) which has been modulated by a spread code. Hence, the modulation performed in the spread modulating part 8-3 is not a modulation by the information signal.
In the spread modulating part 8-3, as shown by (c) of FIG. 2, a ring modulator 9c-1 spreads and modulates an input signal by the spread code consisting of a string of binary code (1, 0), and outputs a spread wave of 150 MHz via a bandpass filter 9c-2.
The power amplifying part 8-4 amplifies the signal outputted from the spread modulating part 8-3 by a power amplifier thereof consisting of one stage or a plurality of stages, and then supplies an power-amplified radio-frequency signal to a transmitting antenna 8-7.
The local-transmitting-frequency generating part 8-5, as shown by (d) of FIG. 2, is a PLL synthesizer which consists of a reference oscillator 9d-1, a phase detector 9d-2, a low-pass filter 9d-3, a voltage-controlled oscillator 9d-4 and a variable frequency divider 9d-5. The local-transmitting-frequency generating part 8-5 generates a local-transmitting-frequency signal corresponding to an inputted local-transmitting-frequency designation signal as a frequency division of the PLL synthesizer, and sends the local-transmitting-frequency signal to the frequency converter 9b-2 of the baseband modulating part 8-2.
In the local-transmitting-frequency generating part 8-5, the phase detector 9d-2 detects a phase difference between a signal from the reference oscillator 9d-1 and a signal from the variable frequency divider 9d-5, and, via the low-pass filter 9d-3, inputs the two signals into the voltage-controlled oscillator 9d-4.
A signal outputted from the voltage-controlled oscillator 9d-4 is inputted into the variable frequency divider 9d-5, in which a frequency of the output signal is divided according to a frequency division designated by the local-transmitting-frequency designation signal and then is transmitted to the phase detector 9d-2.
The spread-code generating part 8-6 generates the spread code designated by a spread-code designation signal and outputs the spread code to the spread modulating part 8-3. The spread code is, for example, a string of binary code (1, 0) of 3 Mbs, and is distributed into each of mobile stations so as to identify each mobile station and spread a transmitting signal sent thereto. The length of the code string is related to an identification code and the length of a bit is related to a width of the spread.
The baseband modulating part 8-2 modulates the communication information signal of the voice, data or the like at a low speed. The spread modulating part 8-3 spreads the transmitting signal according to the identification code of each of the mobile stations and performs a modulation at a middle/high speed.
FIG. 3 is a block diagram illustrating a conventional receiver used for spread spectrum communications. In this diagram, reference numeral 10-1 denotes a receiving baseband processing part, 10-2 a baseband demodulating part, 10-3 a despread modulating part, 10-4 a high-frequency amplifying part, 10-5 a local-receiving-frequency generating part and 10-6 a despread-code generating part. FIG. 4 illustrates respective circuits of these functional parts of FIG. 3.
An antenna 10-7 receives a radio signal and inputs the radio signal into the high-frequency amplifying part 10-4 in which, as shown by (a) of FIG. 4, the inputted radio signal is amplified by passing through a bandpass filter 11a-1, an amplifier 11a-2 and a bandpass filter 11a-3 and then is outputted to the despread modulating part 10-3. The amplifier 11a-2 is formed by a stage of an amplifying circuit or by a plurality of stages of the amplifying circuit.
The despread modulating part 10-3 despreads a spread wave outputted from the high-frequency amplifying part 10-4 so as to shrink the spread wave back to its original signal prior to spreading. In the despread modulating part 10-3, as shown in (b) of FIG. 4, a ring modulator 11b-1 despreads the spread wave of, for example, 3 Mbps, by a despread code formed by a string of binary code (1, 0) so as to converge the spread wave to become a narrowband FM wave of 150 MHz (i.e., in a case in which the narrowband FM has been used).
The baseband demodulating part 10-2 demodulates a basic modulation wave outputted from the despread modulating part 10-3 to produce a baseband signal and outputs this communication information signal of the voice, data or the like to the receiving baseband processing part 10-1. In a case in which the signal to be received by the receiving baseband processing part 10-1 is a digital data signal from the beginning like the individual connection control signal of each mobile station, the digital signal is demodulated and outputted to a logic circuit (not shown).
In a case of demodulating the narrowband FM wave of 150 MHz, in the baseband demodulating part 10-2, as shown by (c) of FIG. 4, a frequency converter 11c-1 uses a local-receiving-frequency signal of 140 MHz to change the frequency of the narrowband FM wave of 150 MHz so that a bandpass filter 11c-2 takes out a signal of 10 MHz and outputs the signal of 10 MHz to an FM demodulator (i.e., a discriminator) 11c-3 in which the signal is demodulated back to the baseband signal.
In a case of demodulating a digital modulated signal, for example, a FSK modulated signal, the baseband demodulating part 10-2 demodulates the digital modulated signal from the frequency signal which has shifted to the plus direction or the minus direction.
The receiving baseband processing part 10-1 processes and outputs the information signal of the voice, data or the like according to whether the baseband demodulating part 10-2 outputs an analog signal or a digital signal.
In a case in which of the output signal is an analog signal, in the receiving baseband processing part 10-1, as shown by (d) of FIG. 4, an integrating circuit 11d-1 integrates the analog signal and output an integrated signal to an amplifier 11d-2, and the amplifier 11d-2 amplifies the integrated signal and outputs an integrated-and-amplified signal to, for example, a speaker or the like. The integrating circuit 11d-1 functions to improve the talk articulation together with the differential circuit 9a-1 of the transmitting side.
In a case in which the output signal is a digital signal, the receiving baseband processing part 10-1 performs a digital-into-analog conversion so as to convert a voice signal or the like into an analog signal and outputs the analog signal.
The local-receiving-frequency generating part 10-5 has the identical constitution with the above-mentioned local-transmitting-frequency generating part 8-5, wherein the local-receiving-frequency signal corresponding to the local-receiving-frequency designation signal is generated and transmitted to the frequency converter 11c-1 of the baseband demodulating part 10-2. The despread-code generating part 10-6 generates a despread code which is identical with the above-mentioned spread code and transmits the despread code to the despread modulating part 10-3.
However, even though the spread spectrum communications can make better use of the frequency, a high speed for processing signals is needed during the spreading and despreading thereof. For this reason, a large-type battery is required to provide sufficient power. As a result, it is difficult to realize a small-size and light-weight mobile station.
The mobile station may perform receiving intermittence so as to reduce the power consumption. However, if the receiving intermittence is too long, a delay may occur in a call connection for a call-in. Hence, there is a limitation on reduction of the power consumption by the receiving intermittence.
A CMOS logic IC consumes little power when an operation speed is low, but as the operation speed increases, the consumed power increases. The consumed power Pr can take the form
Pr=(CL+Cpd)xc2x7fxc2x7Vcc2xe2x80x83xe2x80x83(1)
where CL denotes a load capacity, Cpd denotes an internal equivalent capacity, f denotes an operating frequency, and Vcc denotes a supply voltage.
FIG. 5 is a graph for illustrating characteristics of an operating frequency and a consumed current of the CMOS logic IC. The consumed current is in direct proportion to the operating frequency. The consumed current represents a consumed current per gate. Since a logic circuit portion used by a control circuit of a digital radio machine is formed by several tens of thousands of circuits, the consumed current of the logic circuit portion occupies the majority of the overall consumed current.
As shown in FIG. 5, the consumed current of the logic circuit portion is related to an operation speed. In other words, the operation speed is in proportion to the consumed current. FIG. 6 shows an example of respective frequencies (speeds) and speed ratios of an analog voice signal, a low-speed baseband digital modulation signal and a middle-speed spread signal. With respect to the frequencies (speeds) which influence the consumed current, the analog voice signal and the spread signal cannot be simply compared with each other since the ratio thereof is 500.
With respect to the consumed power, for example, if operating at 3 MHz per gate consumes 5 V and 0.4 mA (2 mW), then a circuit block including 1000 gates will consumes 400 mA. In a case in which an intermittence in which a ratio of receiving operation xe2x80x9cONxe2x80x9d to receiving operation xe2x80x9cOFFxe2x80x9d is 1:9, a consumed current is 40 mA. On the other hand, an analog amplifier can be operated by 1 V, 1 mA (1 mW) even in a case of a high frequency of 150 MHz.
Thus, the baseband processing part and baseband modulation and demodulating parts work at a low speed, and therefore each consumes very little current, whereas the spreading and the despreading work at a high speed and each consumes a large current. Hence, in order to reduce the consumed power of the mobile station, it is important to reduce the consumed power of the spreading and the despreading.
The mobile station has much more wait time than occupation time. Consumed current in the wait time greatly influences the life of the battery, namely, available time of the mobile station. Further, since a receiver of the mobile station used for the spread spectrum communications has to perform the despread modulation all the time even during the wait time, it is difficult to reduce the consumed current.
It is a general object of the present invention to provide a method for spread spectrum communications and a transmitter and receiver of the method, in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a method for spread spectrum communications between a base station and a mobile station and to a transmitter of the base station and a receiver of the mobile station.
The above objects of the present invention are achieved by a method for spread spectrum communications between a base station and a mobile station, comprising the steps of:
(a) controlling a transmitter of the base station to stop a spread modulation so as to transmit a free-line signal and a call-in signal to the mobile station which is in a wait state of waiting to receive the signals;
(b) controlling a receiver of the mobile station to stop a despread modulation in the wait state so as to receive the free-line signal and the call-in signal from the base station; and
(c) controlling the transmitter to modulate, spread, and then transmit and the receiver to receive and then despread and demodulate:
a control signal for connecting a line after transmitting and receiving the call-in signal are completed;
a control signal for connecting the line when a call-out request is sent from the mobile station; and
a communication information signal and a communication-completion control signal which are transmitted and received through the line.
The above objects of the present invention are achieved by a transmitter of a base station for spread spectrum communications, comprising:
a baseband modulating part;
a spread modulating part;
a spread-code generating part; and
a spread control part;
wherein the spread control part stops a spread modulation so as to transmit a free-line signal and a call-in signal which are outputted from the baseband modulating part, and controls the spread modulating part so as to spread modulate and then transmit to a mobile station which is in a wait state:
a control signal for connecting a line after transmitting the call-in signal is completed;
a control signal for connecting the line when a call-out request is sent from the mobile station; and
a communication information signal and a communication-completion control signal which are to be transmitted through the line.
The transmitter may be configured such that the baseband modulating part is a constitution capable of performing a narrowband frequency modulation, and the spread modulating part is a constitution capable of performing a direct sequence spread modulation by the spread code.
The transmitter may be configured such that the baseband modulating part is a constitution capable of performing a digital phase modulation, and the spread modulating part is a constitution capable of performing a direct sequence spread modulation by the spread code.
The above objects of the present invention are achieved by a receiver of a mobile station for spread spectrum communications, comprising:
a baseband demodulating part;
a despread modulating part;
a despread-code generating part; and
a despread control part;
wherein, when the mobile station is in a wait state, the despread control part stops a despread modulation so as to receive a free-line signal and a call-in signal which are transmitted from a base station, and controls the despread modulating part so as to receive and then despread modulate:
a control signal for connecting a line after receiving the call-in signal is completed;
a control signal for connecting the line when a call-out request is sent from the mobile station; and
a communication information signal and a communication-completion control signal which are transmitted through the line.
The receiver may be configured such that the baseband demodulating part is a constitution capable of demodulating a narrowband FM signal and the despread modulating part is a constitution capable of performing a direct sequence despread modulation by a despread code.
The receiver may be configured such that the baseband demodulating part is a constitution capable of demodulating a digital phase modulated signal, and the despread modulating part is a constitution capable of performing a direct sequence despread modulation by the despread code.
As mentioned above, according to the resent invention, in a wait time, the mobile station stops the despread modulation and waits to receive the free-line signal and the call-in signal which are transmitted from the base station. Only during the talk and in the location registration, does the mobile station perform the despread modulation and exchange signals with the base station. Hence, since the consumed power in the wait time can be drastically reduced and the consumed current of a battery can be reduced, it is easy to ensure a long use of the battery and a small-size and produce light-weight mobile station.